1. Field of the Invention
The invention relates to a ratchet screwdriver, more particularly to a high torsion ratchet mechanism assembly for a ratchet screwdriver.
2. Description of the Related Art
Referring to FIGS. 1 to 3, the ratchet mechanism assembly of a conventional ratchet screwdriver is shown to comprise a ratchet housing which includes an elongated substantially cylindrical housing portion 10 having a central bore 101, and an integral extension 102 that projects rearwardly from a closed end of the housing portion 10 and is connected securely to an elongated handle (not shown) of the ratchet screwdriver. The outer surface of the housing portion 10 has a generally I-shaped slot 103 with a transverse rear section 104, and a transverse front section 105. A rotatable drive shaft 11 has a front portion that extends into the bore 101 via an open end of the housing portion 10. A ratchet wheel 110 is connected securely on the front portion of the drive shaft 11. Two ratchet pawls 12 are positioned in the slot 103 in such a manner that wide end portions 121 of the former are received within the transverse front and rear sections 104, 105. Each of the ratchet pawls 12 has a finger portion 122 that extends along the axial section of the slot 103. The ratchet pawls 12 can be engaged with or disengaged from the ratchet wheel 111 by moving a slidable thumb actuator 1 provided within the slot 103 of the housing portion 10. A stop 13 is received in the front section 105 of the slot 103 to abut on the end surface of the ratchet wheel 111 and prevent axial movement of the drive shaft 11 in the housing portion 10.
When assembled, a cylindrical sleeve 3 is slidably mounted on and circumferentially encloses the ratchet housing 10 and the ratchet mechanism therein. A bushing 4 is then installed to close the open end of the housing portion 21.
Because the size of the ratchet screwdriver is relatively small, the contact area between the finger portions 122 of the ratchet pawls 12 and the ratchet wheel 111 is correspondingly small. The conventional ratchet mechanism assembly is thus unsuitable for high-torsion applications. Furthermore, assembly of the conventional ratchet mechanism assembly is inconvenient and relatively complicated.